1. Field of the Invention
This invention relates to an improvement in a solid fuel inflator for an air bag or cushion restraint system that is provided on the passenger side of an automotive vehicle and is characterized by providing "leveled performance" throughout the range of ambient temperatures over which the inflator is intended to be operative while maintaining a "thrust neutral" configuration. The invention is further characterized in allowing the use of a "wrap-around" bag construction.
2. Description of the Prior Art
Some terminology herein is used for convenience in reference only and is not intended to be limiting. The words "forwardly" and "rearwardly" refer to the normal forward and reverse directions of travel of the vehicle to which a passenger restraint module is attached.
By the term "leveled performance" is meant equivalent occupant restraint over the ambient temperature range -30.degree. C. to +85.degree. C.
By the term "bell mouthing" is meant deformation of the module housing or reaction canister tending to be caused by the rapid lateral expansion of the air bag before it has escaped the confines of the module housing or reaction canister in which it has been stored.
The term "thrust neutral" refers to the production by an inflator for an air bag of zero thrust when accidentally initiated as, for example, during shipping, storage and handling, as well as during activation responsively to the onset of a collision. Specifically, the gas discharge orifices of the inflator are so positioned around the periphery of the inflator that the gas is discharged in opposing directions whereby there are no resulting forces tending to cause movement thereof. Thus, the inflator will expend the energy generated thereby generally in place.
It is known in the prior art to provide an inflatable restraint system including an air bag which is expanded by a solid fuel inflator to restrain movement of an occupant of an automotive vehicle in the event of a collision. The inflator is designed to rapidly generate a quantity of gas sufficient to inflate the bag. It has been found, however, that in very cold weather the inflator attains its peak pressure much less rapidly than in warm weather. Thus, in cold weather, there is a tendency for the air bag to be inflated either too slowly or insufficiently to perform its intended purpose. Inflator performance such as this which varies with ambient temperature can cause discomfort or possible injury to the vehicle occupant who relies upon inflation of the air bag for protection.
U.S. Pat. No. 4,380,346, L. E. Davis et al., assigned to the assignee of the present invention, discloses an elongated cylindrical air bag inflator for the passenger side of an automotive vehicle and characterized in providing uniform operation in both cold and warm weather in a thrust neutral configuration. In this arrangement the orifices or passages in the inflator housing are all of uniform size and a multiple strength rupturable foil is provided in association therewith to allow selected ones of the orifices to open at a low pressure, and other orifices to open at a higher pressure.
While the Davis et al. arrangement is thrust neutral, it is subject to a disadvantage in that all of the generated gases flow rearwardly into the air bag. The increased deployment forces on the stored air bag and module housing at the higher temperatures tend to cause deformation, that is, bell mouthing of the module housing and to tear the air bag upon deployment thereof.
U.S. Pat. No. 4,817,828, G. W. Goetz, discloses an inflatable restraint system for the passenger side of an automotive vehicle including an elongated cylindrical inflator. Provided on one side of the housing for the inflator are a plurality of orifices or passages of a first size which are arranged to direct generated gases rearwardly into an air bag. A plurality of orifices of a second and smaller size is provided on the opposite side of the housing for directing gas forwardly away from the bag into the vehicle compartment or into a conduit leading to the surrounding environment. A foil on the inside wall of the inflator housing ruptures adjacent the larger orifices of the first size at a pressure that is lower than the pressure at which the foil ruptures at the smaller orifices of the second size. The first and second pluralities of orifices are blocked by the foil prior to activation of the inflator. Upon activation of the inflator, the foil adjacent the plurality of orifices of the first size ruptures when a sufficient pressure builds up in the inflator to allow generated gases to flow into the air bag. Thus, the air bag is not subjected to relatively low pressure which would tend to cause the air bag to be inflated slowly in cold weather. If the pressure in the inflator is too high, which tends to occur when the ambient temperature is high, the second and smaller size orifices open when the foil seal covering them is ruptured to direct gas away from the air bag. As a result, the air bag is not subjected to excessive pressure because of high ambient temperatures.
Although the Goetz patent provides for directing generated gases away from the air bag when the temperature is high, it is subject to a disadvantage in that it does not provide for a thrust neutral configuration. In the absence of a thrust neutral configuration, the thrust produced by the deployment forces must be absorbed by the module housing in which the stored air bag and inflator are contained and also by the dashboard of the automotive vehicle in which the occupant restraint system is installed. Such thrust tends to cause damage not only to the module housing but also to the dashboard of the vehicle. Additionally, the arrangement of the Goetz patent does not allow the inflator to be cooperatively positioned with respect to the air bag in a wrap-around configuration.
Also known in the prior art is an elongated cylindrical solid fuel thrust neutral inflator assembly, as schematically illustrated in FIGS. 1 and 2 of the drawings, the internal construction of which is generally similar to that of the aforementioned Davis et al. patent. The inflator assembly there shown, designated by the reference numeral 10, includes first, second and third pluralities of orifices 12, 14 and 16, respectively, from which, upon activation of the inflator 10, generated gases flow under pressure and are directed rearwardly into an air bag (not shown). The cross sections of the first, second and third pluralities of orifices are all of different size.
Prior to activation of the inflator 10, a rupturable foil 18 on the inside of the housing 20 therefor, as seen in FIG. 2, blocks all of the orifices. The first plurality of orifices 12, those having the largest area, are opened to allow gas to flow into the air bag when a sufficient pressure builds up in the inflator 10 to rupture the portions of the 18 adjacent thereto. Thus, the air bag is not subjected to a relatively low pressure that could cause the air bag to be slowly or otherwise improperly inflated under cold weather conditions.
If the pressure internally of the inflator continues to rise, as tends to occur upon an increase in the ambient temperature, the second plurality of orifices 14, those having an area of intermediate size, open to direct gas into the air bag as the result of rupture of the portions of the foil 18 adjacent thereto. This relieves the inflator internal pressure and thus avoids subjecting the air bag to an abnormally high deployment force. Similarly, if the ambient temperature continues to rise to +85.degree. C., the orifices 16 having the smallest area also open when the pressure in the inflator rises sufficiently to rupture the portions of foil 18 adjacent those orifices. Opening of the orifices 16 also causes generated gas to be directed into the air bag and the internal pressure within the inflator 10 to be additionally relieved. This tends to avoid subjecting the air bag to excessive pressures because of the high ambient temperature.
The first, second and third pluralities of orifices 12, 14 and 16 open at different internal pressures of the inflator 10. The foil portions 18 covering the largest of the orifices ruptures first because those orifices have the largest area exposed to the inflator pressure. The portions of foil 18 covering the orifices having the largest area rupture at a pressure lower than the foil portions adjacent the orifices 14 of intermediate area. Similarly, the foil portions covering the orifices 14 of intermediate area rupture at a lower pressure than the portions of foil 18 adjacent the orifices 16 having the smallest area.
The inflator assembly 10 disclosed in FIGS. 1 and 2, similarly to that disclosed in the Davis patent, is subject to a disadvantage in that all of the solid fuel generated gases over the entire range of operation flow rearwardly into the air bag. The resulting increased deployment forces on the air bag and on the module (not shown) employed to house the inflator at the higher temperatures, particularly, tend to cause bell mouthing of the module housing and to tear the air bag during deployment.
Thus, there is a need and a demand for an improved solid fuel inflator for air bag restraint systems having utility on the passenger side of automotive vehicles to the end of providing leveled performance throughout the range of ambient temperatures over which the inflator is intended to be operative while maintaining a thrust neutral configuration, and further, which is characterized in allowing the use of a wrap-around air bag configuration. The present invention was devised to fill the gap that has existed in the art in these respects.